Detector circuit



Nov. 5, 1935. R. M. PAGE 2,019,503

DETECTOR CIRCUIT Filed oct. 16, 1954 K I O M "'0 o a W. n

mvzm'on 1 Roberi M. Pa e Patented Nov. 5, 1935 UNITE TT F 2 Claims.

(Granted under the act of March 3, 1883, as

amended April 30, 1928; 3'70 0. G. 757) This invention relates to a calibrator and more particularly to a calibrator employing a piezoelectric crystal oscillator together with means for deriving from said oscillator a considerable num- 5 her of harmonic frequencies which, by reason of their constant frequency characteristics, may be employed in accurately calibrating electricalcircuits.

The principal object of this invention is to provide a circuit arrangement for deriving from a crystal oscillator a great number of harmonically related frequencies. a

Another object of this invention is to provide a calibrator circuit arrangement in which a frequency derived from a circuit being calibrated is combined with one of the harmonic frequencies derived from an oscillator and the resultant beat frequency is detected in such a manner as to provide an extremely low background noise. Other and further objects will be apparent from the following specification and drawing wherein the single figure shows schematically a preferred embodiment of the invention.

In the drawing the part of the circuit under bracket A represents a crystal oscillator system; part B represents a distorting amplifier; part C represents a detector; while part D represents a two-stage audio frequency amplifier with phone connections. The crystal oscillator A, consisting of an electron tube I having a piezo-electric crystal 2 connected between cathode and control grid and an inductance 3 having a high ratio of inductance to distributed capacity connected in series with a source of anode potential between the anode and cathode of the tube, is a more or less conventional type of crystal oscillator similar to the oscillator disclosed by Owens in Patent 1,673,200.

The output of the oscillator is fed by way of the condenser 4 to the input circuit of the distorting amplifier B. The distorting amplifier consists of an electron tube 5 having a cathode, an anode, and a control electrode, the control electrode of which is connected to the cathode by way of a radio frequency choke coil 5, and the anode of which is connected to the cathode by way of a second radio frequency choke coil 1 connected in series with a source of anode potential IS. The output of the distorting amplifier is fed by way of the condenser a to the input circuit of the detector C.

The detector C consists of an electron tube 9 having a cathode, an anode, and a control electrode, the control electrode of which is con- 5 nected to the cathode by way of the resistor l2,

the slider I9 and the potentiometer resistor l8, and the anode of which is connected to the cathode by way of the primary winding of an audio frequency transformer It, the slider l9 and the potentiometer resistor !8. it connected between terminal H and the control electrode of the tube 9 serves as a radio frequency path for the frequencies to be calibrated which are impressed at terminal II. It is to be noted that the anode of the detector tube 9 has 10 no auxiliary source of anodepotential connected between it and the cathode for maintaining the anode at a high positive potential but that the potential drop derived from that portion of the potentiometer resistor i8 included between the 1d slider l9 and the cathode is the only potential impressed on the detector anode, and this potential is of such a magnitude and direction as to maintain the anode at zero potential with respect to the positive cathode lead or at a po- 20 tential slightly more negative than any part of the cathode depending upon the position of the slider I9 and the relative sizes of the batteries I6 and H. A radio frequency bypass condenser I3 is connected between the anode and 2 the cathode of the detector tube 9.

The output of the detector C is amplified by a suitable audio frequency amplifying system D shown as consisting of amplifying tubes 20 and 2! together with associated apparatus and the 30 amplified signals are impressed upon a pair of phones 23 or other suitable signal observing means. A bypass condenser 22 is connected in shunt with the source of anode potential iii.

The operation of the calibrator is as follows: 35 The crystal oscillator A delivering a standard frequency rich in harmonics is used to energize the distorting amplifier B which due to the operation of the radio frequency choke coils 5 and l delivers harmonics of the crystal as high as the two thousandths or higher to the detector C upon whose control circuit the radio frequency to be measured is impressed by way of terminal II. The frequency being measured will be combined with some one of the harmonics of the crystal standard to produce a beat note of audible frequency. This beat note is then amplified by a suitable audio frequency amplifier and the amplified audio frequency note may be observed in the phones 23. 50

The extremely great range of harmonics of this system is due in part to the distorting amplifier and in part to the detector anode circuit. The distorting amplifier accentuates the upper harmonies of the crystal and increases the ampli- Condenser 5 tude of all the harmonics to such a point that a detector of the type employed may be used. The particular detector employed reduces the background noise and the signal derived from harmonics of low order is reduced. This reduction is desirable, for the signal amplitude derived from those harmonics is normally excessive. The signals from the higher harmonics, on the other hand, are actually increased by elimination of the conventional detector anode battery, due to further distortion thus produced in the detector of the higher harmonics developed in the distorting amplifier.

Many modifications may be made in the system disclosed without departing from the principle of this invention. Multiple grid tubes may be used in the amplifiers, and a different oscillator circuit may be employed. In certain cases it may be desirable to connect a high frequency choke between the condenser 4 and the choke coil 5 in order to prevent the extremely high frequency voltages developed in the distorting amplifier from being shunted to ground through the ground capacity of the anode and the high potential lead from the oscillator and the distributed capacity of the coil 3.

The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

I claim:

1. A detector for detecting the beat frequency components resulting from the combination of a signal frequency to be calibrated and a plutombs rality of harmonically related frequencies which comprises a thermionic tube having a cathode, an anode and a control electrode, means for impressing said frequencies upon the control electrode, means for biasing said control electrode 5 with respect to said cathode, an audio frequency output device connected in circuit between the anode and the cathode of said tube, said circuit between the anode and cathode of said tube including therein means for maintaining the steady potential of said anode at a value not greater than thepotential of said cathode, and a bypass condenser connected between the anode and the cathode of said tube.

2. A detector for detecting the beat frequency components resulting from the combination of a signal frequency to be calibrated and a plurality of harmonically related frequencies which comprises a thermionic tube having a cathode, an anode and a control electrode, means for impressing said frequencies upon the control electrode, means for biasing said control electrode with respect to said cathode, an audio frequency output device connected in circuit between the anode and the cathode of said tube, said circuit between the anode and cathode of said tube including therein means for maintaining the steady potential of said anode at a value not greater than the potential of said cathode, and a by-pass condenser connected between the anode and the cathode of said tube, and means for varying the value of the potential difference between the anode and the cathode.

- ROBERT M. PAGE. 35 

